1. Field of the Invention
The present invention relates generally to an air conditioning and/or refrigerating system and more more specifically to a refrigeration arrangement for use therein which includes a waste heat powered jet pump.
2. Description of the Prior Art
In automotive air conditioning systems which employ a mechanically driven compressor a drawback is encountered in that the operation of the compressor places an additional load on the engine of the vehicle, which both increases the amount of fuel which is combusted and reduces the power available at the driven wheels of the vehicle. This problem is particularly evident in large buses, refrigerator trucks and the like, wherein the demand for air conditioning and/or refrigeration is particularly high.
In order to overcome this problem it has been proposed to utilize the waste heat of the engine in a Rankine cycle arrangement in manner which permits the load on the engine per se to be reduced.
FIG. 1 shows one example of the above mentioned systems which was disclosed in Japanese Patent Application First Provisional Publication No. 57-134668. As shown, this arrangement comprises a boiler 1 which includes a heating coil and which is partially filled with a refrigerant liquid. The coil 2 is operatively connected with the engine (not shown) and arranged so that heated fluid such as exhaust gas or engine coolant is passed therethrough. During engine operation the liquid refrigerant in the boiler 1 is heated to the degree that it boils and produces high temperature and pressure refrigerant vapor.
The high pressure and temperature refrigerant vapor produced in the boiler 1 passes through a first conduit 4 and is introduced into an ejector or jet pump 6 via a nozzle 8. The jet of vapor which issues from the nozzle 8 induces a low pressure in a mixture chamber 10 which surrounds the nozzle and induces a flow of fluid from an evaporator 12 to enter the chamber. The inducted fluid is subsequently carried along with the vapor ejected from the nozzle 8 to a condenser 14.
The condenser 14 in this instance takes the form of a heat exchanger through which a fan forced daft of air is induced to flow.
A small reservoir 16 in which the condensate from the condenser is collected and temporarily stored is disposed downstream of the condenser 14. A return pump 18 inducts the liquid refrigerant from the reservoir 16 and pumps the same back into the boiler 1. The evaporator 12 communicates with the conduit 20 interconnecting the reservoir 16 and the pump 18 via an expansion valve 22. The valve 22 permits a fraction of the liquid refrigerant flowing through the conduit 20 to be lead into the evaporator 12 wherein it expands and absorbs the heat contained in a flow of air passing through the devices. In this instance the evaporator 12 is included in an automotive cabin air conditioning arrangement and the flow of air directed thereinto via a suitable flow control and ducting arrangement.
This device, while reducing the load on the engine by utilizing the waste heat which is released therefrom into the engine coolant or which is contained in the exhaust gases, has suffered from the drawbacks that:
With ejection type compressor arrangements the compression possible is small compared with a mechanically driven compressor and in order to obtain the best performance it is necessary to ensure that the pressure of the vapor fed into the nozzle 8 is high while the pressure in the condenser 14 is maintained low. Viz., as the compressor in this case takes the form of a heat engine, it is necessary to ensure that the temperature differential between the heat source and the heat sink is as large as possible. However, as the temperature of the high pressure vapor ejected from the nozzle 8 is high, the temperature of the condensate recycled to the evaporator 12 tends to become elevated after a brief period of operation. This tends increase the temperature of the liquid refrigerant entering the evaporator 12, reduce temperature to which the heat exchanging surfaces of the evaporator 12 can be lowered and thus reduce the amount of heat which can be removed from the air passing through the evaporator.
By way of example, if the working fluid of the above arrangement is selected to be FREON R11 or FREON 114 it is possible to lower the temperature of the evaporator 12 to 10.degree. C. However, this level is not adequate and further requires the temperature in the condenser to be held at or below 40.degree. C.
In the event that the ambient temperature is 30.degree. C., the temperature differential between the cooling medium and the minimum temperature requirements of the condenser 14, is small and greatly hampers the removal of the necessary amount of heat therefrom.
In order to compensate for the above, it is necessary to avoid reductions in the condensation capacity (heat exchange capacity) of the condenser 14. However, as pointed out above, as the ambient atmospheric temperature increases the temperature differential between the heat exchanging surfaces and the cooling medium decreases whereby the amount of heat which can be removed from the condenser is decreased. In order to ensure that acceptable operation is obtained (viz., the required amount of heat can be absorbed and released) the size of both the condensor and the evaporator have to be enlarged. This increases the weight and bulk of the system undesirably. However, even when large scale condensers and evaporators are used, still there tend to be instances wherein the operational characteristics become unacceptable. For example when the ambient temperature rises to 40.degree. C. or above.